Disease relevance of Mgat3

• To investigate a functional role for the bisecting GlcNAc in the development of liver cancer, the Mgat3 gene that codes for GlcNAc-TIII, was inactivated by targeted gene disruption, and the susceptibility of Mgat3-/- mice to tumor induction was tested [1].
• Our previous studies showed that the transfection of the GnT-III gene into B16 melanoma cells results in a suppression of invasive ability and lung colonization [2].
• Suppression of lung metastasis of B16 mouse melanoma by N-acetylglucosaminyltransferase III gene transfection [3].
• These results suggest that the glycosylated E-cadherin contributes to the suppression of metastasis by the introduction of GnT-III gene into melanoma cells [4].
• We found that forskolin, an adenylyl cyclase activator, markedly enhanced GnT-III at the transcriptional level in various hepatoma cells and hepatocytes, resulting in an increase of bisecting GlcNAc residues in various glycoproteins, as judged from the lectin binding to erythroagglutinating phytohemagglutinin (E-PHA) [5].

High impact information on Mgat3

• Ectopic expression of N-acetylglucosaminyltransferase III in transgenic hepatocytes disrupts apolipoprotein B secretion and induces aberrant cellular morphology with lipid storage [6].
• These abnormal phenotypes were more prominent in the mice with more copies of the transgene and a resulting high GnT-III activity [6].
• Because PB aids tumor progression, we tested whether it diminished the difference in tumor progression between Mgat3(+/+) and Mgat3(Delta/Delta) mice [7].
• N-acetylglucosaminyltransferase III (GlcNAc-TIII) is encoded by the Mgat3 gene and catalyzes the addition of the bisecting GlcNAc to the core of N-glycans [8].
• New evidence for an extra-hepatic role of N-acetylglucosaminyltransferase III in the progression of diethylnitrosamine-induced liver tumors in mice [8].

Chemical compound and disease context of Mgat3

• Using B16-hm mouse melanoma cells stably expressing GnT-III activity as positive transfectants, the effect of bisecting N-acetylglucosamine on the function of CD44 was analyzed in association with adhesion to hyaluronate and tumor spread in mice [9].

Biological context of Mgat3

• Using fluorescence in situ hybridization (FISH), the Mgat3 gene was regionally mapped to chromosome 15E11, near the Scn8a sodium channel gene at 15F1 [10].
• Assays for Mgat3 gene expression in tumor tissue gave an unexpected result [1].
• Southern analysis showed that Mgat3 is present in a single copy in the mouse genome [11].
• The deduced amino acid sequence of the Mgat3 gene expressed in each CHO mutant and in parent CHO genomic DNA is identical [12].
• We show that three CHO mutants, LEC10, LEC10A, and LEC10B, arose due to transcriptional activation of the quiescent CHO Mgat3 gene [12].

Anatomical context of Mgat3

• Somatic cell hybrid analysis indicated that the LEC10B Mgat3 gene was induced by a cis mechanism [12].
• The LEC10 gain-of-function Chinese hamster ovary (CHO) cell mutant that expresses GlcNAc-TIII and complex N-glycans with the bisecting GlcNAc was used to immunize Mgat3(+/+) and Mgat3(-/-) mice [13].
• GnT-III activity is elevated during hepatocarcinogenesis, which is in contrast to the undetectable level found in normal hepatocytes [6].
• The overexpression of GnT-III, but not that of an enzymatic inactive GnT-III (D323A), inhibits cell spreading and migration on fibronectin, a specific ligand for integrin alpha(5)beta(1), and the focal adhesion kinase phosphorylation [2].
• In the transgenic mice, the GnT-III activity was elevated in bone marrow, spleen and peripheral blood and in isolated mononuclear cells from these tissues, whereas no activity was found in these tissues of wild-type mice [14].

Associations of Mgat3 with chemical compounds

• Isolation, characterization and inactivation of the mouse Mgat3 gene: the bisecting N-acetylglucosamine in asparagine-linked oligosaccharides appears dispensable for viability and reproduction [10].
• In the absence of the bisecting GlcNAc in Mgat3-/- mice, the factor is reduced in activity, and tumor progression is severely retarded [1].
• However, histological examination showed that Mgat3-/- livers had significant numbers of basophilic foci, and by 10-12 months after diethylnitrosamine injection, tumors had developed in Mgat3-/- mice [1].
• Following DEN injection and phenobarbitol treatment, however, no significant differences were observed between MUP/Mgat3 transgenic and control mice in either tumor numbers or liver weight [8].
• E(4)-PHA lectin blot analyses showed that the levels of bisecting GlcNAc structures on the integrin alpha(5) subunit as well as alpha(2) and alpha(3) subunits immunoprecipitated from GnT-III transfectants were substantially increased [2].

Regulatory relationships of Mgat3

• In addition, tyrosine phosphorylation of beta-catenin by transfection of constitutively active c-src was suppressed in GnT-III transfectants as well as in the case of epidermal growth factor stimulation [15].
• E-cadherin expression at cell-cell contacts of B16-hm cells expressing high GnT-III activity was greater than controls without affecting transcription [4].
• Expression of GnT-III also suppressed the antigenicity of MEC to human natural antibodies as shown by binding of Griffonia simplicifolia 1 isolectin (GS1B4 lectin) to the alpha-Gal epitope [16].

Other interactions of Mgat3

• The overexpression of GnT-III in the cells led to the induction of axon-like processes with numerous neurites and swellings, in which beta1 integrin was localized, under conditions of serum starvation [17].
• Introduction of the beta1-4 N-acetylglucosaminyltransferase (GnT-III) gene was reported to suppress metastasis in highly metastatic B16-hm murine melanoma cells (Yoshimura, M., Nishikawa, A. , Ihara, Y., Taniguchi, S., and Taniguchi, N.(1995) Proc. Natl. Acad. Sci. U. S. A. 92, 8754-8758) [4].
• Furthermore, cell-cell aggregation was enhanced in GnT-III transfectants, indicating that the glycosylated E-cadherin is biologically functional [4].
• Immunoprecipitation followed by E4-PHA lectin blot analysis also confirmed that the bisecting GlcNAc, a product of GnT-III was added to haptoglobin molecules [18].

Analytical, diagnostic and therapeutic context of Mgat3

• ELISA of whole sera showed that polyclonal antibodies that bound specifically to LEC10 cells were obtained solely from Mgat3(-/-) mice [13].
• Fluorescence-activated cell cytometry of different CHO glycosylation mutants and western blotting after glycosidase treatments were used to show that anti-LEC10 cell antisera from Mgat3(-/-) mice recognize cellular glycoproteins with complex N-glycans containing both a bisecting GlcNAc and Gal residues [13].
• Introduction of the GnT-III gene resulted in an increase of bisecting GlcNAc and a decrease of external sialic acid as well as tri- and tetraantennary sugars, as judged by flow cytometry [19].
• In addition, we demonstrated the effect of GnT-III in down-regulating the xenoantigen of pig heart grafts, using a pig to cynomolgus monkey transplantation model, suggesting that this approach may be useful in clinical xenotransplantation in the future [20].
• N-acetylglucosaminyltransferase III, IV and V activities in Novikoff ascites tumour cells, mouse lymphoma cells and hen oviduct. Application of a sensitive and specific assay by use of high-performance liquid chromatography [21].

References